1. Field of the Invention
The present invention relates to a developer supplying device, a developing roller, a developing device, an image forming apparatus and a process cartridge.
2. Discussion of the Background
A developing device 200 illustrated in FIG. 14 has been used as a single component developer system using a single component developer. Such a single component developer contains a toner. This developing device 200 includes a developing roller 208 formed of an elastic body and a developer supplying roller 206, which is abrasively in contact with the developing roller 208, to supply a developer (i.e., toner) 204 thereto. In addition, the developing device 200 further includes a layer thickness regulating member 207, a developer holding unit 203 to hold the developer, and an agitator 205 functioning as an agitating member. The layer thickness regulating member 207 is in contact with the developing roller 208 to reduce the thickness of the developer layer on the developing roller 208. The agitator 205 supplies the developer to the surface of the developer supplying roller 206 while stirring the developer in the developer holding unit 203.
In this developing device 200, the developer 204 held in the developer holding unit 203 is agitated by the agitator 205 and mechanically supplied to and borne on the surface of the developer supplying roller 206. The developer supplying roller 206 bears and transfers the developer 204 at a portion opposing the developing roller 208 while the developer supplying roller is in abrasive contact with the developing roller 208. The developer 204 supplied to the developing roller 208 forms a developer layer on the surface thereon and the thickness of the developer layer is suitably regulated by the layer thickness regulating member 207. In addition, the developer 204 is friction-charged with a desired polarity and is transferred at a portion opposing an image bearing member 1, i.e., the developing area, by the rotation of the developing roller 208 in the direction indicated by the arrow in FIG. 14.
However, in the developing device 200 as illustrated in FIG. 14, the developer 204 is mechanically agitated by the agitator 205 and transferred to the developer supplying roller 206. Therefore, the developer 204 is mechanically stressed by the agitator 205. In addition, in the developing device 200, the layer thickness regulating member 207 is in contact with the developing roller 208 with a high pressure to abrasively charge the developer 204 to a desired polarity. Thereby, the developer 204 receives significant mechanical stress when the developer 204 passes the layer thickness regulating member 207.
Typically, inorganic additives are attached around the mother binder resin of a toner to improve fluidity thereof. These additives sink in the mother binder resin by the mechanical stress mentioned above, resulting in deterioration of the fluidity of the toner. Therefore, the toner agglomerates and the amount of charge in the toner decreases, which has an adverse impact such as background fouling and poor toner supply.
In an image forming apparatus including the developing device using a single component developer mentioned above, the toner easily deteriorates and it is thus difficult to obtain images having good quality over an extended period of time. Further, since the toner supplying roller and the regulating member are in abrasive contact with the developing roller, the developing roller is abraded and toner attachment, i.e., filming, occurs. Consequently, it is difficult to maintain the durability of the developing device over an extended period of time.
Published unexamined Japanese Patent Application No. (hereinafter referred to as JOP) H05-232800 describes a technology in which a toner transferred from a transfer screw is supplied to a fur brush and further transferred to the outer surface of the developing roller by the rotation of the fur brush. The toner is abrasively charged with the inner wall of the casing and the fur brush while the toner is transferred by the fur brush. Thereby, the charged toner is supplied to the surface of the developing roller. That is, the toner is abrasively charged by the rotation of the fur brush during transfer. Thereby, the mechanical stress on a toner can be relatively small in comparison with that in a method for a typical developing device in which a toner is abrasively charged when the toner passes between a layer thickness regulating member and a developing roller that are in contact under a high pressure.
However, since the toner is transferred by the rotation of a fur brush, meaning that the toner is transferred with a mechanical stress, the toner possibly deteriorates due to the mechanical stress from the fur brush.